This invention relates generally to linear motor positioning and motion systems and methods, and more particularly to an improved linear hybrid brushless servo motor having high force density, high electrical power conversion ratio, and considerably low manufacturing cost.
Conventional linear brushless permanent magnet (PM) servo motors used in the prior art have either an ‘iron-less design’, comprising slot-less moving coil parts and a plurality of permanent magnets on stationary iron core plates (as described in U.S. Pat. No. 6,160,327), or an ‘iron-core design’ comprising a laminated iron core having slots and teeth and phase winding coils in the moving part and a plurality of permanent magnets on the stationary iron-core plate (as described in U.S. Pat. No. 5,642,013, U.S. Pat. No. 5,910,691 and U.S. Pat. No. 6,242,822). The iron-less design has the advantage of zero cogging, zero attractive force and very little mass in the moving part. This design can provide high velocities and high acceleration/deceleration(s) during dynamic motion, but the thrust force is substantially limited because of the big air-gap. The iron-less design also exhibits low force density and low power conversion ratio due to being slot-less and having a relatively big air-gap. Finally, this design is not cost effective due to the need for many high-cost, high energy product, rare-earth permanent magnets. The iron-core design, on the other hand, has high electromagnetic interaction and coupling between the high performance ferromagnetic laminated primary part with slots and winding coils and the high energy product permanent magnets on the stationary ferromagnetic plate so as to have high force density and power conversion ratio in the motor. It also allows the motor to generate high thrust force and provide high velocity and acceleration/deceleration during dynamic motion. It's high manufacturing cost as well as its use of many high-cost rare-earth permanent magnets, however, makes it inherently more expensive than motors using fewer or no magnets, such as stepper motors, induction motors and variable reluctance motors especially for applications necessitating long motion stroke. Moreover, the iron-core design generates high cogging forces due to interactions between the polarity transition portions of the permanent magnets and both the slots and motor end effects in the primary part. Some technologies (such as those disclosed in U.S. Pat. No. 5,642,013 and U.S. Pat. No. 5,910,691) try to minimize the parasitic cogging force in linear iron-core brushless motors. However, they do not eliminate the need to use magnet track plates comprising many high cost rare earth permanent magnets, which results in the high cost of manufacturing motors with such designs.